Cellulose nanofibers and method for producing same, composite resin composition, molded body

ABSTRACT

Cellulose nanofibers have an average degree of polymerization of 600 or more to 30000 or less, an aspect ratio of 20 or more to 10000 or less, an average diameter of 1 nm or more to 800 nm or less, and an Iβ-type crystal peak in an X-ray diffraction pattern, in which a hydroxyl group is chemically modified by a modifying group.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of and the benefit of Japanese PatentApplication No. 2011-185040 filed on Aug. 26, 2011, and is a continuousapplication of international application PCT/JP2012/069038 filed on Jul.26, 2012, the disclosures thereof are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to cellulose nanofibers, a method forproducing the same, a composite resin composition, and a molded body.

2. Description of Related Art

Cellulose nanofibers have been used as a reinforcing material of apolymer composite material in the related art.

The cellulose nanofibers are generally obtained by mechanically shearingcellulose fibers such as pulp or the like, however, in recent years, amethod for defibrating a fibrous raw material using an ionic liquid hasbeen proposed (Japanese Unexamined Patent Application, First PublicationNo. 2009-179913).

In the method disclosed in Japanese Unexamined Patent Application, FirstPublication No. 2009-179913, since it is not necessary to sufficientlyperform mechanical shearing, there is no concern that the fibers aredamaged, and the method is excellent in terms of its ability to easilyobtain cellulose nanofibers with high strength and high aspect ratio.

Further, a method for modifying a hydroxyl group of cellulose nanofibersby a modifying group in order to increase affinity with a polymercomposite material has been proposed (Japanese Unexamined PatentApplication, First Publication No. 2009-144262).

The method disclosed in Japanese Unexamined Patent Application, FirstPublication No. 2009-144262 excels in terms of improving affinity withpolymer composite materials and showing excellent dispersibility byforming a graft on the surface of the cellulose nanofibers usingpolyvinyl acetal.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, cellulosenanofibers have an average degree of polymerization of 600 or more to30000 or less, an aspect ratio of 20 or more to 10000 or less, anaverage diameter of 1 nm or more to 800 nm or less, and an Iβ-typecrystal peak in an X-ray diffraction pattern, and a hydroxyl group whichis chemically modified by a modifying group.

According to a second aspect of the present invention, in the firstaspect, a thermal decomposition temperature of the cellulose nanofibersmay be equal to or more than 330° C.

According to a third aspect of the present invention, in the firstaspect or the second aspect, a saturated absorptivity of the cellulosenanofibers in an organic solvent having an SP value of 8 or more to 13or less may be 300% or more to 5000% or less by mass.

According to a fourth aspect of the present invention, in the thirdaspect, the organic solvent may be a water-insoluble solvent.

According to a fifth aspect of the present invention, in any one of thefirst aspect to the fourth aspect, the hydroxyl group of the cellulosenanofibers may be esterified or etherified by the modifying group.

According to a sixth aspect of the present invention, in any one of thefirst aspect to the fifth aspect, a modification rate of the cellulosenanofibers may be 0.01% or more to 50% or less based on all of thehydroxyl groups.

According to a seventh aspect of the present invention, a compositeresin composition may contain the cellulose nanofibers according to anyone of the first aspect to the sixth aspect in a resin.

According to an eighth aspect of the present invention, a molded bodymay be formed by molding the composite resin composition according tothe seventh aspect.

According to a ninth aspect of the present invention, a method forproducing cellulose nanofibers may include a process of: swelling acellulose raw material in a solution containing an ionic liquid; andadding a modifier thereto, filtering, and washing the cellulose rawmaterial.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates results of analyzing X-ray diffraction of cellulosenanofibers according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[Cellulose nanofibers]

The average degree of polymerization of cellulose nanofibers accordingto an embodiment of the present invention is in the range of from 600 to30000, preferably in the range of from 600 to 5000, and more preferablyin the range of from 800 to 5000. In the case where the average degreeof polymerization is 600 or more, sufficient reinforcement efficacy canbe obtained. For example, such cellulose nanofibers can be produced by amethod using an ionic liquid. In the case where the average degree ofpolymerization is 30000 or less, a problem such that kneading withresins is difficult to perform does not occur, because the viscosityduring the kneading does not become high.

The aspect ratio of the cellulose nanofibers according to the embodimentof the present invention is 20 to 10000, and preferably 20 to 2000, fromthe viewpoint of reinforcement efficacy. The term “aspect ratio” of thepresent specification and claims means the ratio of an average fiberlength to an average diameter (average fiber length/average diameter) incellulose nanofibers. In the case where the aspect ratio is 20 or more,sufficient reinforcement efficacy can be obtained. Further, the aspectratio is 10000 or less, moldability of a composite resin compositioncontaining the cellulose nanofibers is excellent. Furthermore, theaspect ratio is in the range described above, in the cellulosenanofibers, the entanglement between molecules and the network structurebecome strong, thereby improving the mechanical strength of a moldedbody.

The average diameter of the cellulose nanofibers according to theembodiment of the present invention is 1 nm to 800 nm, preferably 1 nmto 300 nm, and more preferably 1 nm to 100 nm. In the case where theaverage diameter thereof is 1 nm or more, the cost for production islow, and in the case where the average diameter thereof is 800 nm orless, the aspect ratio thereof is hard to decrease. As a result,sufficient reinforcement efficacy can be obtained at low cost.

A cellulose type I is composite crystals of Iα-type crystals and Iβ-typecrystals, and cellulose derived from high-grade plants such as cottonincludes a large quantity of Iβ-type crystals, on the other hand,bacteria cellulose includes a large quantity of Iα-type crystals.

Since the cellulose nanofibers according to the embodiment of thepresent invention include an Iβ-type crystal peak in an X-raydiffraction pattern, the X-ray diffraction pattern indicates a patternunique to the Iβ-type crystals as shown in FIG. 1.

Further, since the cellulose nanofibers according to the embodiment ofthe present invention mainly includes the Iβ-type crystals, thereinforcement efficacy thereof is excellent when compared to thebacteria cellulose with a large quantity of Iα-type crystals.

The cellulose nanofibers according to the embodiment of the presentinvention are chemically modified for improving functionality. In orderto use the cellulose nanofibers as a composite material, it is necessaryto chemically modify hydroxyl groups on the surface of the cellulosenanofibers by a modifying group so as to reduce the number of thehydroxyl groups. The cellulose nanofibers are easily dispersed into apolymer material by preventing strong adherence between cellulosenanofibers due to hydrogen bonds, and therefore, excellent interfacialbonds can be formed between the cellulose nanofibers and the polymermaterial.

The ratio of the hydroxyl groups, which are chemically modified by amodifying group, to the total hydroxyl groups in the cellulosenanofibers according to the embodiment of the present invention ispreferably 0.01% to 50%, more preferably 10% to 30%, and particularlypreferably 10% to 20%.

It is preferable that a hydroxyl group be etherified or esterified bythe modifying group in view of convenience and high efficiency.

Preferred examples of etherification agents may include an alkyl halidesuch as methyl chloride, ethyl chloride, or propyl bromide; dialkylcarbonate such as dimethyl carbonate, or diethyl carbonate; dialkylsulfate such as dimethyl sulfate or diethyl sulfate; and alkylene oxidesuch as ethylene oxide or propylene oxide. Further, the etherificationis not limited to alkyl etherification caused by the aboveetherification agents, and aralkyl etherification caused by benzylbromide, silyl etherification, and the like are preferable.

Examples of silyl etherification agents may include alkoxysilane, andspecific examples thereof may include alkoxysilane such as n-butoxytrimethylsilane, tert-butoxytrimethylsilane, sec-butoxytrimethylsilane,isobutoxytrimethylsilane, ethoxytriethylsilane,octyldimethylethoxysilane, or cyclohexyloxytrimethylsilane,alkoxysiloxane such as butoxypolydimethylsiloxane, and disilazane suchas hexamethyldisilazane, tetramethyldisilazane, ordiphenyltetramethyldisilazane. In addition, silyl halides such astrimethylsilyl chloride or butyl diphenyl silyl chloride, and silyltrifluoromethane sulfonate such as t-butyldimethylsilyl trifluoromethanesulfonate may also be used.

Examples of esterification agents include a carboxylic acid that mayinclude a hetero atom, a carboxylic acid anhydride, and a carboxylichalide. As the esterification, an acetic acid, a propionic acid, abutyric acid, an acrylic acid, a methacrylic acid and derivativesthereof are preferred, and an acetic acid, acetic anhydride, and butyricanhydride are more preferable.

Alkyl etherification, alkyl silylation, and alkyl esterification fromamong etherification and esterification are preferable for improvingdispersibility into a resin.

In the case where the cellulose nanofibers which are chemically modifiedin this way are used for a lipophilic resin, it is preferable that thesaturated absorptivity of the cellulose nanofibers in an organic solventwith a solubility parameter (hereinafter, referred to as an “SP value”)of 8 or more to 13 or less is 300% by mass to 5000% by mass. Thecellulose nanofibers which are dispersed in the organic solvent havingthe above-described SP value have high affinity with a lipophilic resin,and high reinforcement efficacy.

Examples of the organic solvents having an SP value of 8 or more to 13or less may include an acetic acid, ethyl acetate, butyl acetate,isobutyl acetate, isopropyl acetate, methyl propyl ketone, methylisopropyl ketone, xylene, toluene, benzene, ethyl benzene, dibutylphthalate, acetone, 2-propanol, acetonitrile, dimethylformamide,ethanol, tetrahydrofuran, methyl ethyl ketone, cyclohexane, carbontetrachloride, chloroform, methylene chloride, carbon disulfide,pyridine, n-hexanol, cyclohexanol, n-butanol, and nitromethane.

As the organic solvent, a water-insoluble solvent (a solvent that is notmixed with water of 25° C. at an arbitrary ratio) is more preferable,and examples thereof may include xylene, toluene, benzene, ethylbenzene, dichloromethane, cyclohexane, carbon tetrachloride, methylenechloride, ethyl acetate, carbon disulfide, cyclohexanol, andnitromethane. The cellulose nanofibers which are chemically modified inthe above way can be dispersed in a water-insoluble solvent, and easilydispersed in a lipophilic resin in which the conventional cellulosenanofibers are hard to disperse.

Since the cellulose nanofibers according to the embodiment of thepresent invention have heat resistance by being chemically modified, itis possible to impart the heat resistance to other materials by allowingthe cellulose nanofibers to be mixed with other materials.

The thermal decomposition temperature of the cellulose nanofibersaccording to the embodiment of the present invention is preferably 330°C. or more, and more preferably 350° C. or more. A thermal decompositiontemperature of 330° C. or more is too high temperature for conventionalcellulose nanofibers to withstand.

The degree of crystallinity of the cellulose nanofibers having theabove-described structure according to the embodiment of the presentinvention is 80% or more. Accordingly, the cellulose nanofibersaccording to the embodiment of the present invention have exceedinglyexcellent reinforcement efficacy on resins.

[Composite Resin Composition]

The composite resin composition according to the embodiment of thepresent invention includes the cellulose nanofibers in a resin.

As the above-described lipophilic resin in which the cellulosenanofibers according to the embodiment of the present invention can bedispersed, a resin which is sparingly soluble in water and widely usedas an industrial material for which water resistance is needed ispreferable. The lipophilic resin may be a thermoplastic resin or athermosetting resin, and examples thereof may include a plant-derivedresin, a resin using carbon dioxide as a raw material, anacrylonitrile-butadiene-styrene (ABS) resin, an alkylene resin such aspolyethylene or polypropylene, a styrene resin, a vinyl resin, anacrylic resin, an amide resin, an acetal resin, a carbonate resin, anurethane resin, an epoxy resin, an imide resin, a urea resin, a siliconeresin, a phenol resin, a melamine resin, an ester resin, an acrylicresin, an amide resin, a fluorine resin, a styrole resin, andengineering plastic. In addition, as the engineering plastic, polyamide,polybutylene terephthalate, polycarbonate, polyacetal, modifiedpolyphenylene oxide, modified polyphenylene ether, polyphenylenesulfide, polyether ether ketone, polyether sulfone, polysulfone,polyamide imide, polyether imide, polyimide, polyarylate, or polyallylether nitrile is preferably used. Further, two or more kinds of theseresins may be used as a mixture. Among these, polycarbonate isparticularly good due to its high impact strength.

As the polycarbonate, generally used polycarbonate can be used. Forexample, aromatic polycarbonate which is produced by reacting anaromatic dihydroxy compound and a carbonate precursor can be preferablyused.

Examples of the aromatic dihydroxy compound may include2,2-bis(4-hydroxyphenyl)propane (“bisphenol A”),bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane,2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 4,4′-dihydroxydiphenyl,bis(4-hydroxyphenyl)cycloalkane, bis(4-hydroxyphenyl)sulfide,bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide,bis(4-hydroxyphenyl)ether, and bis(4-hydroxyphenyl)ketone.

Examples of the carbonate precursor may include a carbonyl halide,carbonyl ester, and a haloformate, and specific examples thereof mayinclude phosgene, dihaloformate of a dihydric phenol, diphenylcarbonate, dimethyl carbonate, and diethyl carbonate.

As the polycarbonate used in the embodiment of the present invention,polycarbonate that does not contain an aromatic group may be used. Asthe polycarbonate that does not contain an aromatic group, alicyclicpolycarbonate or aliphatic polycarbonate are exemplary examples. Apolycarbonate resin may be linear or branched. In addition, thepolycarbonate resin may be a copolymer of a polymer, which is obtainedby polymerizing the aromatic dihydroxy compound and the carbonateprecursor, and other polymers.

The polycarbonate resin may be produced by a conventionally knownmethod, and examples thereof may include an interfacial polymerization,a melt transesterification method, a pyridine method, and the like.

As the types of the resin in the composite resin composition accordingto the embodiment of the present invention, a hydrophilic resin may beincluded in addition to the lipophilic resin described above. Withregard to the hydrophilic resin, unmodified cellulose nanofibers, andcellulose nanofibers which are chemically modified by a hydrophilicfunctional group such as a sulfonic acid group, a carboxylic acid groupand these chlorides may be preferably used due to high dispersibilityinto the hydrophilic resin.

As the hydrophilic resin, polyvinyl alcohol and a resin which issubjected to a hydrophilic treatment are listed as examples. Amongthese, polyvinyl alcohol is particularly preferred for its low cost andhigh dispersibility of the cellulose nanofibers. The composite resincomposition according to the embodiment of the present invention mayinclude an additive such as a filler, a flame retardant aid, a flameretardant, an antioxidant, a release agent, a colorant, or a dispersantin addition to those described above.

Examples of the filler to be used may include a carbon fiber, a glassfiber, clay, titanium oxide, silica, talc, calcium carbonate, potassiumtitanate, mica, montmorillonite, barium sulfate, a balloon filler, abead filler, and a carbon nanotube.

Examples of the flame retardant to be used may include a halogen-basedflame retardant, a nitrogen-based flame retardant, a metal hydroxide, aphosphorous based-flame retardant, an organic alkali metal salt, anorganic alkali earth metal salt, a silicone-based flame retardant, andexpanded graphite.

As the flame retardant aid, polyfluoroolefin, antimony oxide, or thelike may be used.

As the antioxidant, a phosphorous-based antioxidant, a phenyl-basedantioxidant, or the like may be used.

As the mold release agent, higher alcohol, carboxylic acid ester, apolyolefin wax, or polyalkylene glycol may be used.

As the colorant, an arbitrary colorant such as carbon black orphthalocyanine blue may be used.

As the dispersant, a dispersant in which the cellulose nanofibers can bedispersed in a resin may be used, and examples thereof may include ananionic, cationic, nonionic, or amphoteric surfactant, and a polymerdispersant, and these may be used in combination.

Since the cellulose nanofibers according to the embodiment of thepresent invention have reinforcement efficacy as described above, thecomposite resin composition containing the cellulose nanofibersaccording to the embodiment of the present invention is excellent interms of strength. Therefore, the composite resin composition accordingto the embodiment of the present invention is suitable for use in anapplication requiring strength.

Further, since the cellulose nanofibers according to the embodiment ofthe present invention have excellent dispersibility in a resin, thecomposite resin composition containing the cellulose nanofibersaccording to the embodiment of the present invention is excellent interms of transparency. Accordingly, the composite resin compositionaccording to the embodiment of the present invention can maintain itstransparency, and therefore the composite resin composition is suitablefor use in an application requiring transparency.

Furthermore, since the cellulose nanofibers according to the embodimentof the present invention have excellent heat resistance when compared tothe cellulose nanofibers in the related art, the composite resincomposition containing the cellulose nanofibers according to theembodiment of the present invention is excellent in terms of heatresistance. Therefore, the composite resin composition according to thepresent invention is suitable for use in an application requiring heatresistance while maintaining transparency.

[Molded Body]

The molded body according to the embodiment of the present invention isformed by molding the composite resin composition. The method formolding the molded body is not particularly limited, but examplesthereof may include various conventionally known methods such as aninjection molding method, an injection compression molding method, anextrusion molding method, a blow molding method, a press molding method,a vacuum molding method, and a foam molding method.

Since the molded body according to the embodiment of the presentinvention contains the cellulose nanofibers according to the embodimentof the present invention, the strength or the heat resistance thereof isexcellent. As the molded body, although not particularly limited,medical equipment, audio equipment, or the like are listed as examples.Such a molded body may be used for a molded body for a camera, a lensbarrel, or the like, which particularly requires strength.

[Method for Producing Cellulose Nanofibers]

A method for producing cellulose nanofibers according to the embodimentof the present invention includes a process of swelling a cellulose rawmaterial in a solution containing an ionic liquid, adding a modifierthereto, filtering, and washing the resultant.

The method for producing the cellulose nanofibers according to theembodiment of the present invention is a method for performing a processof defibrating a cellulose raw material in a solvent containing an ionicliquid and a process of chemically modifying a hydroxyl group of thecellulose nanofibers using a modifying agent in one step (hereinafter,referred to a one-step method).

In the process of defibrating the cellulose raw material in a solventcontaining an ionic liquid, the solution in which the cellulose rawmaterial is dissolved is thickened. Consequently, in the method forproducing the cellulose nanofibers using an ionic liquid in the relatedart, a sulfate treatment hydrolyzing a low crystalline cellulose partusing sulfate is necessary in order to decrease the viscosity thereof,therefore, a method for performing a process of defibration and aprocess of chemical modification in two steps (hereinafter, referred toas a “two-step method”) has been used.

Since the one-step method according to the embodiment of the presentinvention has a fewer number of processes compared to the two-stepmethod in the related art, the one-step method has advantages in termsof management and cost. In addition, the amount of a solvent being usedis small, so that the burden on the environment may be reduced.

The cellulose raw material according to the embodiment of the presentinvention is not particularly limited, however, examples thereof mayinclude raw materials of natural cellulose such as linter, cotton, andhemp; pulp obtained by chemically treating wood such as kraft pulp orsulfide pulp; semi-chemical pulp; used paper or recycle pulp thereof,and the like. Among these, pulp obtained by chemically treating wood ispreferable, linter with high average degree of polymerization is morepreferable when the cost, quality, and the burden on the environment areconsidered.

The shape of the cellulose raw material is not particularly limited,however, it is preferable that the cellulose raw material is used afterbeing appropriately pulverized from the viewpoints of easiness ofmechanical sheerness and accelerating permeation of solvents.

As the solution containing the ionic liquid (hereinafter, referred to asa treatment solution), a solution containing an ionic liquid representedby the following chemical formula 1 and an organic solvent ispreferable.

[In the formula, R¹ represents an alkyl group having 1 to 4 carbonatoms, R² represents an alkyl group having 1 to 4 carbon atoms or anally! group. X″ represents a halogen ion, pseudo-halogen, carboxylatehaving 1 to 4 carbon atoms, or thiocyanate.]

Examples of the ionic liquid may include 1-butyl-3-methylimidazoliumchloride, 1-butyl-3-methylimidazolium bromide,1-allyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazoliumbromide, and 1-propyl-3-methylimidazolium bromide.

It is also possible to defibrate the fiber raw material using only theionic liquid, however, in the case where even fine fibers are likely tobe dissolved due to excessively high solubility, it is preferable to addan organic solvent to the ionic liquid for use.

The type of the organic solvent to be added may be selected inconsideration of compatibility with the ionic liquid, affinity withcellulose, solubility of a mixed solvent, viscosity, and the like, andparticularly, it is preferable to use any one or more of organicsolvents from among N,N-dimethylacetamide, N,N-dimethylformamide,1-methyl-2-pyrrolidone, dimethylsulfoxide, acetonitrile, methanol, andethanol.

Since the production method according to the embodiment of the presentinvention is a one-step method which does not include a process of asulfate treatment, the ionic liquid after the defibration treatment doesnot contain a hydrolytic agent. Therefore, recycling of the ionic liquidafter the defibration treatment is easy to perform.

The amount of the ionic liquid in the treatment solution may beappropriately adjusted since the amount of the ionic liquid depends onthe types of the cellulose raw material, the ionic liquid, and theorganic solvent, but the amount thereof is preferably 20% by mass ormore from the viewpoints of swelling and solubility. In the case wherean organic solvent having high solubility is used, the amount thereof ispreferably 30% by mass or more, and in the case where an organic solventhaving low solubility such as methanol is used, the amount thereof ispreferably 50% by mass or more.

The amount of the cellulose raw material is preferably in the range of0.5% by mass to 30% by mass based on the treatment liquid. In view ofeconomic efficiency, the amount thereof is preferably 0.5% by mass ormore, and more preferably 1% by mass or more. In view of uniformity ofthe defibration degree, the amount thereof is preferably 30% by mass orless, and more preferably 20% by mass.

In the method for producing the cellulose nanofibers according to theembodiment of the present invention, the cellulose raw material isswollen in the solution containing an ionic liquid. The cellulose rawmaterial is constituted by crystalline cellulose with high degree ofcrystallinity, and a binding substance including lignin which is presentbetween the crystalline cellulose, hemicellulose, and amorphouscellulose. The fine structure constituting cellulose is somewhatslackened by swelling the cellulose raw material, and enters a state inwhich it can be easily cleaved by the external force.

According to the embodiment of the present invention, a process ofadding a modifier to the cellulose raw material in such a state,filtering, and washing the resultant is included.

As the modifier used in the production method according to theembodiment of the present invention, the same modifier as described inthe method of producing the cellulose nanofibers according to theembodiment of the present invention may be used.

In the method for producing cellulose nanofibers according to theembodiment of the present invention, it is possible to obtain cellulosenanofibers having the properties described in the cellulose nanofibersaccording to the embodiment of the present invention.

That is, according to the embodiment of the present invention, it ispossible to obtain cellulose nanofibers having an average degree ofpolymerization of from 600 to 30000, an aspect ratio of 20 to 10000, anaverage diameter of 1 nm to 800 nm, and an Iβ-type crystal peak in anX-ray diffraction pattern, in which a hydroxyl group is chemicallymodified by a modifying group.

Further, according to the embodiment of the present invention, since theprocess of a sulfide treatment is not included, there is no concern thatthe cellulose nanofibers are damaged, cellulose nanofibers having heatresistance with a thermal decomposition temperature of 330° C. or morecan thereby be obtained.

Furthermore, the obtained cellulose nanofibers have high degree ofcrystallinity. The reason why such effects can be obtained is not clear,but it can be speculated as follows.

In the process of defibration in the solution containing an ionicliquid, the cellulose raw material is swollen in the solution containingan ionic liquid. That is, the fine structure constituting cellulose issomewhat slackened and enters a state in which it can be easily cleavedby the external force. Here, among three hydroxyl groups which arepresent in the constituent unit of the cellulose, one hydroxyl group isexposed to the surface of the cellulose, and the other two hydroxylgroups are assumed to be related to formation of the crystal structure.In the one-step method for the present invention, since a modifier isdirectly added to the swollen crystalline cellulose, it is speculatedthat the hydroxyl group exposed to the surface of the cellulose isefficiently modified.

In the two-step method, amorphous cellulose or the like, which isunnecessary, present in the cellulose raw material is removed while theswollen cellulose raw material is being hydrolyzed by the sulfatetreatment.

On the other hand, in the one-step method according to the embodiment ofthe present invention, it can be speculated that since a hydroxyl groupis hydrophobized and amorphous cellulose becomes easily dissolved in asolvent by modifying the hydroxyl group of the swollen amorphouscellulose, the hydroxyl group is therefore easily removed by filtration.

EXAMPLES

Hereinafter, the embodiment of the present invention will bespecifically described by Examples and Comparative Examples, but theembodiment of the present invention is not limited to the followingExamples.

Example 1

15 g filter paper cut into a 3 mm square with scissors was put into a300 ml flask, and then 100 ml of N,N-dimethylacetamide and 100 g of anion liquid 1-butyl-3-methylimidazolium chloride were added to the flask,followed by stirring. Subsequently, 90 g of acetic anhydride was addedthereto to react with each other, and filtered to wash the solidcontent. The resultant was treated with a homogenizer, thereby obtainingacetylated cellulose nanofibers by the one-step method. The modificationrate of the acetylated cellulose nanofibers obtained at this time was17%, and the thermal decomposition temperature thereof was 350° C.

Subsequently, polycarbonate which was dissolved in dichloromethane inadvance (PC, manufactured by Teijin Chemicals Ltd., Panlite L-1225L,refractive index: 1.58) was mixed with the acetylated cellulosenanofibers in the dichloromethane, and then dried, thereby obtaining apolycarbonate composite resin composition containing the acetylatedcellulose nanofibers.

Example 2

Butylated cellulose nanofibers in which the one-step method was used anda polycarbonate composite resin composition containing the butylatedcellulose nanofibers were obtained by the same procedures as Example 1except that butyric anhydride was added instead of acetic anhydride. Themodification rate of the butylated cellulose nanofibers obtained at thistime was 12% and the thermal decomposition temperature thereof was 350°.

Example 3

Silylated cellulose nanofibers in which the one-step method was used anda polycarbonate composite resin composition containing the silylatedcellulose nanofibers were obtained by the same procedures as Example 1except that hexamethyl disilazane was added instead of acetic anhydride.The modification rate of the silylated cellulose nanofibers obtained atthis time was 15% and the thermal decomposition temperature thereof was350° C.

Example 4

Propylated cellulose nanofibers in which the one-step method was usedand a polycarbonate composite resin composition containing thepropylated cellulose nanofibers were obtained by the same procedures asExample 1 except that propyl bromide was added instead of aceticanhydride. The modification rate of the propylated cellulose nanofibersobtained at this time was 15% and the thermal decomposition temperaturethereof was 350° C.

Reference Example 1

2 g filter paper cut into a 3 mm square with scissors was put into a 200ml flask, and then 50 ml of N,N-dimethylacetamide and 60 g of an ionliquid 1-butyl-3-methylimidazolium were added to the flask, followed bystirring. Subsequently, a sulfuric acid aqueous solution was addedthereto, stirred, and filtered to wash the solid content. The resultantwas treated with a homogenizer, thereby obtaining cellulose nanofibersby the two-step method. The obtained cellulose nanofibers were reactedwith acetic anhydride to be acetylated, and the resultant was washed,thereby obtaining acetylated cellulose nanofibers. The modification rateof the acetylated cellulose nanofibers obtained at this time was 17%,and the thermal decomposition temperature thereof was 320° C.

Subsequently, polycarbonate which was dissolved in dichloromethane inadvance (PC, manufactured by Teijin Chemicals Ltd., Panlite L-1225L,refractive index: 1.58) was mixed with the acetylated cellulosenanofibers in the dichloromethane, and then dried, thereby obtaining apolycarbonate composite resin composition containing the acetylatedcellulose nanofibers.

Reference Example 2

Butylated cellulose nanofibers in which the two-step method was used anda polycarbonate composite resin composition containing the butylatedcellulose nanofibers were obtained by the same procedures as Example 1except that butyric anhydride was added instead of acetic anhydride. Themodification rate of the butylated cellulose nanofibers obtained at thistime was 16% and the thermal decomposition temperature thereof was 320°C.

Comparative Example 1

A polycarbonate composite resin composition was obtained by the samemethod as Reference Example 1 and using bacteria cellulose nanofibersobtained by drying Nata de COCO (manufactured by Fujicco Co., Ltd.,average degree of polymerization: 3000 or more, average aspect ratio:1000 or more, average diameter: 70 nm).

Comparative Example 2

A polycarbonate composite resin composition was obtained by the samemethod as Reference Example 1 and using fine crystalline cellulose(manufactured by Merck Ltd., average degree of polymerization: 250,average aspect ratio: 10, crystals having a diameter of 1 μm to 10 μmare mixed).

The cellulose nanofibers and the composite resin compositions obtainedfrom respective Examples, Reference Examples, and Comparative Exampleswere measured by the following test method, and the results thereof arelisted in Table 1.

(1) Measurement of Average Degree of Polymerization

The molecular weight was evaluated by viscometry (reference:Macromolecules, volume 18, page 2394 to 2401, 1985).

(2) Aspect ratio and Average Diameter

The number average fiber diameter and the number average length of thecellulose nanofibers were evaluated by SEM analysis.

Specifically, a cellulose nanofiber dispersion was cast on a wafer so asto be observed by SEM. The values of fiber diameter and length were readout with respect to 20 or more strands of fibers for each of theobtained images. This operation was performed on at least 3 sheets ofimages of non-overlapping regions, thereby obtaining information on thediameter and length of a minimum of 30 strands of fibers.

From the data of the diameter and the length of the fibers obtained asabove, the number average fiber diameter and the number average lengthcould be calculated, and the aspect ratio was then calculated from theratio of the number average length to the number average fiber diameter.In the case where the aspect ratio was in the range of from 20 to 10000,it was indicated as excellent, and in the case where the aspect ratiowas not in the range of from 20 to 10000, it was indicated as poor.

(3) Crystal Structure Analysis (XRD)

The crystal structure of the cellulose nanofibers was analyzed using apowder X-ray diffractometer Rigaku Ultima IV. In the case where thecrystal structure of the cellulose nanofibers was an Iβ-type crystalstructure, it was indicated as ∘ (excellent), and in the case where thecrystal structure of the cellulose nanofibers was not the Iβ-typecrystal structure, it was indicated as × (poor) in Examples, ReferenceExamples, and Comparative Examples.

(4) Thermal Decomposition Temperature (TG-DTA)

The cellulose nanofibers were measured using a thermal analysisapparatus THERMO plus TG8120. A graph in which the weight decreasingrate was plotted on vertical axis and the temperature was plotted on thehorizontal axis was drawn, and the temperature of the intersection pointof a tangent at the time when the weight was largely reduced and atangent before the weight was reduced was set to the thermaldecomposition temperature.

(5) Evaluation Method for Modification Rate Al of Hydroxyl group

The modification rate of the hydroxyl group was calculated from astrength of corresponding characteristic band/a strength ofcharacteristic band of CH (before and after 1367 cm⁻¹) in the cellulosering by FT-IR. For example, in the case where a C═O group (before andafter 1736 cm⁻¹) was obtained by modification, the value in which thestrength thereof was divided by the strength of CH was obtained, andthen the modification rate was calculated by standard curve that wascreated by a quantitative measurement method such as NMR or the like inadvance.

(6) Evaluation of Saturated Absorptivity R

First, cellulose nanofibers of a weight (W1) were dispersed indimethylacetamide (SP value: 11.1), thereby preparing a dispersion of 2%by weight. Subsequently, the dispersion was put in a centrifuge flask,followed by centrifugation for 30 minutes at 4500 G, and a transparentsolvent layer in the upper portion of the centrifuged dispersion wasremoved, and then a weight (W2) of a gel layer in the lower portion ofthe centrifuged dispersion was measured, thereby calculating thesaturated absorptivity by the following formula.

R=W2/W1×100%

In the case where the saturated absorptivity was in the range of from300% by mass to 5000% by mass, it was indicated as ∘ (excellent).

TABLE 1 Reference Reference Comparative Comparative Example 1 Example 2Example 3 Example 4 Example 1 Example 2 Example 1 Example 2Polymerization 800 800 800 800 800 800 3000 250 degree Aspect ratio 100100 100 100 50 50 1000 10 Average 30 30 30 30 30 30 70 1000 diameter(nm) Crystal ∘ ∘ ∘ ∘ ∘ ∘ x ∘ structure Thermal 350 350 350 350 320 320300 300 decomposition temperature (° C.) Modification 17 12 15 15 17 160 0 rate A1 (%) Saturated ∘ ∘ ∘ ∘ ∘ ∘ x x absorptivity R (%)

As shown in Table 1, the composite resin compositions of Examples 1 to 4and Reference Examples 1 and 2 were excellent in terms of the saturatedabsorptivity. In addition, the composite resin compositions of Examples1 to 4 in which the cellulose nanofibers produced by the one-step methodwas used were excellent in terms of the thermal decompositiontemperature.

The molded bodies of the respective Examples, Reference Examples, andComparative Examples were measured by the following test method, and theresults thereof were listed in Table 2.

(1) Moldability

The obtained composite resin compositions containing the cellulosenanofibers were thermally melted and molded, and the molded state wasdetermined by visual observation. “o” indicates cases where themoldability was excellent, and “×” indicates cases where the moldabilitywas poor.

(2) Linear Thermal Expansion Coefficient

A linear thermal expansion coefficient between 100° C. and 180° C. wasmeasured using Thermo plus TMA8310 (manufactured by Rigaku Corporation)in an air atmosphere at a heating rate of 5° C./min. The size of a testsample was set to 20 mm (length)×5 mm (width). First, a first-run wascarried out at a temperature range of room temperature to Tg, and thenthe temperature was cooled to room temperature and a second-run iscarried out. From the results, a linear thermal expansion coefficientwas calculated by the following formula.

Linear thermal expansion coefficient(%)=(length at a time point of 180°C.−length at a time point of 40° C.)/length at a time point of 40°C.×100

In the case where the linear thermal expansion coefficient was 5% ormore, it was indicated as o (excellent), and in the case where thelinear thermal expansion coefficient was less than 5%, it was indicatedas × (poor).

TABLE 2 Reference Reference Comparative Comparative Example 1 Example 2Example 3 Example 4 Example 1 Example 2 Example 1 Example 2 Moldability∘ ∘ ∘ ∘ ∘ ∘ x x Linear ∘ ∘ ∘ ∘ ∘ ∘ ∘ x thermal expansion coefficient

As shown in Table 2, the molded bodies of Examples 1 to 4 showedmoldability and linear thermal expansion coefficient superior to thoseof the molded bodies of Comparative Examples 1 and 2.

Furthermore, the entire components described in the above-mentionedembodiments, and various modified examples can be carried out bysuitably changing or deleting the combination within the scope of thetechnical idea of the invention.

While preferred embodiments of the present invention have beendescribed, the present invention is not limited to the embodiments.Additions, omissions, substitutions, and other variations may be made tothe present invention within the scope that does not depart from thescope of the present invention. The present invention is not limited bythe above description, but only by the appended claims.

1. Cellulose nanofibers, having an average degree of polymerization of600 or more to 30000 or less, an aspect ratio of 20 or more to 10000 orless, an average diameter of 1 nm or more to 800 nm or less, and anIβ-type crystal peak in an X-ray diffraction pattern, wherein a hydroxylgroup is chemically modified by a modifying group.
 2. The cellulosenanofibers according to claim 1, wherein a thermal decompositiontemperature of the cellulose nanofibers is equal to or more than 330° C.3. The cellulose nanofibers according to claim 2, wherein a saturatedabsorptivity of the cellulose nanofibers in an organic solvent having anSP value of 8 or more to 13 or less is 300% or more to 5000% or less bymass.
 4. The cellulose nanofibers according to claim 3, wherein theorganic solvent is a water-insoluble solvent.
 5. The cellulosenanofibers according to claim 1, wherein the hydroxyl group of thecellulose nanofibers is esterified or etherified by the modifying group.6. The cellulose nanofibers according to claim 1, wherein a modificationrate of the cellulose nanofibers is 0.01% or more to 50% or less basedon all of the hydroxyl groups.
 7. A composite resin composition,comprising the cellulose nanofibers according to claim 1 in a resin. 8.A composite resin composition, comprising the cellulose nanofibersaccording to claim 3 in a resin.
 9. A molded body which is formed bymolding the composite resin composition according to claim
 8. 10. Amethod for producing cellulose nanofibers, comprising a process of:swelling a cellulose raw material in a solution containing an ionicliquid; and adding a modifier thereto, filtering, and washing thecellulose raw material.
 11. The cellulose nanofibers according to claim1, wherein a saturated absorptivity of the cellulose nanofibers in anorganic solvent having an SP value of 8 or more to 13 or less is 300% ormore to 5000% or less by mass.